Partition and characterization of cadmium on different particle-size aggregates in Chinese Phaeozem

Abstract Organic-mineral complexations can be isolated from bulk soil by physical disaggregation followed by density fractionation for further examination of the patchy nature of aggregates distributed in soil. Phaeozem, which is a specific regional soil in China with high organic matter, was selected for fractionation into particle-size aggregates with clay, silt, fine sand and coarse sand. Partition and characterization of the adsorbed Cd in the bulk soil and various aggregates of Phaeozem were investigated by Fourier-transform infrared (FTIR) spectrometry, X-ray diffraction (XRD) and sequential extraction. The results indicated that Cd could be differently partitioned into various particle-size aggregates, which could be characterized by FTIR and XRD with the same results. Clay had the highest adsorption capacity for the relevant high content of montmorillonite, kaolinite and chlorite, as well as organic matter and cation exchange capability. The fine fraction had the greatest potential availability and mobility of Cd because it was primarily absorbed on the surface of kaolinite. The texture of Phaeozem likely contributed to the metal fate and behavior in the soil environment, as well as other properties such as organic matter, cation exchange capacity and surface area.